Bring a large pot of water to a boil over medium-high heat and season the water with 2 teaspoons of salt. Boil the rotini for 1 minute less than package directions until al dente and reserve ¼ cup starchy pasta water. Then strain and set aside.

Heat olive oil in a large pan over medium heat. Sauté garlic for 10 seconds, then cook chicken until browned on the edges. Set aside.

Melt butter in the same pan and sauté mushrooms until softened and golden.

Add heavy cream and reserved pasta water. Simmer until the sauce thickens enough to coat a spoon.

Stir baby spinach into the sauce until just wilted.

Remove the pan from heat, add rotini, and toss until evenly coated.